The devices of this invention are intended to improve the fastening of roof systems to decks in those cases where the fasteners penetrate the deck. Examples of such decks are plywood. Tectum (shredded wood with a cement binder), hollow concrete panels, and metal decks, the use of metal decks being the most preferred. Metal decks are normally twenty two gauge steel and primarily, metal anchor screws which are used to hold down roof systems, are manufactured out of various metal alloys in an attempt to provide strength, self tapping capabilities and provide some corrosion resistance. The fasteners are generally stronger than the substrate to which they are applied. Failure of these devices occurs in the pull-out from the substrate rather than destruction of the screw itself, which screws are nominally three sixteenths of an inch in diameter for most roof systems. A secondary weakness of a roof system is at the top side where the materials, such as insulation or roofing membranes tear through the heads and washers of such devices causing the materials to be torn off the top of the roof system. As indicated supra, one advantage of metal screws is that they are self-tapping which means they can be installed in one operation, that is, the entire roof system is laid down in its multiple layers and then fastened with one of the screw type devices by penetrating from the top layer and forcing the screw down into the roof deck where it is screwed into the roof deck for securing the entire roof system. The environment into which these screws are applied can be detrimental to them. For example, installing a roofing system over an existing roof system traps moisture which creates a wet environment setting up rusting and galvanic corrosion of the screws. Further, in a new roof system where subsequent leakage creates a wet environment, there is also set up the same type of rusting and galvanic corrosion environment. The fasteners, even if they are manufactured from stainless steel, do not resist the corrosive atomospheres found within built up roof systems. Also, in those situations where the fasteners are covered with coatings to protect them, the protective coatings tend to be scraped off when they pass through the metal deck and this scraping is more egregious when they have to be passed through an existing built-up roof topped with a stone layer. Further, the protective coating is worn away over short periods of time owing to the constant movement of the roof system due to wind and thermal expansion and contraction. This leaves the metal of the screw vulnerable to corrosion.
Even for those screws that do not require a protective coating the metal deck itself is cut through during installation, exposing the thickness of the metal deck to corrosion with the same subsequent result that is, pull-out of the fastener from the deck.
When considering the screws of small diameter such as the small metal screws currently used in prior art systems the pull-out strength is essentially about 500 pounds regardless of the relative diameter of the screw. This translates directly to the ultimate strength of the system and is the maximum strength of the decking since only one thread of the screw is engaged in the nominally twenty two gauge deck. Metal decks of this gauge have an ultimate strength of two thouand pounds and in order to take advantage of this strength to hold the roof system down, there should be a spreading of the load on the underside of the deck to about at least a three quarter inch diameter interface of the hold down device with the underside of the deck. Thus, in the roofing industry, the five hundred pound limit has become the design criteria for determining the quantity of fasteners and the placement of fasteners to hold the roofing systems in place. The normal pull-out resistance requirements are related to loadings of sixty to ninety pounds per square foot. Ninety is becoming the most sought after requirement with some requirements being raised to one hundred and twenty pounds per square foot. By way of example, and using a pull-out strength of five hundred pounds and the requirement for ninety pounds per square foot the area of roof that can be held down per fastener, on average, is four to five square feet. Typically this means that fastener placement patterns which require eight fasteners are used to hold the systems down which are nominally four feet by eight feet, or thirty two square feet. For roofing membranes which are nominally five feet wide, the nailing pattern at the ends of the runs, and the nails applied on one foot centers throughout the membrane, provide the ability of using about five square feet per fastener. Most often the requirement is to fasten both the insulation and the membrane so that the fastener design approaches one per three square feet.
The fasteners of the instant invention have higher pull-out strengths, that is about two thousand pounds or about four times the five hundred pounds for the devices of the prior art. One fastening device, especially useful in the laminar roofing industry, is a piercing type of screw device, which is made to pierce the lamelle of the roof structure by screwing it downwardly into the metal roof deck. These type of devices all rely on spiral threads. Eventhough these devices are made with a minimum pitch in the thread, still only one portion of the thread comes into contact with the surface around the pierced hole of the metal deck. The use of this type of device gives a "can opener" effect whereby the screw is pointed and when it pierces the metal, it cleaves away the metal. They are completely devoid of any annular rings or toggles, or the like, around the bottom to help secure them in the hole. Also there is a problem with having the length of such a device correspond exactly with the thickness of the laminar roof in order to get the maximum securing strength.
Fastening devices having the configuration of anchor bolts are also generally known which consist of a bolt or stem which is treaded, has a cap or head portion on one end and a nut or toggle on the opposite end whereby after insertion through an opening the nut or toggle is screwed down on the threaded bolt or stem and the device tightens from both ends to secure the object between them. In a rather sophisticated arrangement of one such device, such as that found in U.S. Pat. No. 3,667,340 to Daniel A. Black, et al., there is illustrated a fastening device in the nature of a rivet wherein a tubular sleeve has a head on one end bearing against one side of the work piece, and an internally threaded tail. A screw is extended through the head and the sleeve is threaded into said tail and is so positioned that the screw head is initially spaced from the head of the sleeve; the shank of the sleeve is slotted and the resulting strips are notched internally at about the middle so that by turning the screw the tail travels toward the head and the strips are folded flat against the other face of the workpiece. In the method of making this fastener, after the hollow rivet with the head is formed it is positioned in a die and cutting blades are forced through the wall of the sleeve to cut parallel longitudinal slots dividing the middle portion of the sleeve into strips of arcuate cross section, then the sleeve is held in a die while a tool is inserted and rotated to cut a groove into the strips for facilitating the collapsing of the sleeve. Then the screw is inserted into the sleeve and the tail of the sleeve is pressed or swaged into the screw to form the internal thread in the tail and hold the screw. The shank between the sleeve head and the adjacent ends of the slots is approximately equal to the minimum thickness in which the fastener is used. The sleeve head has a recess in both faces to accommodate suitable washers. Thus, with reference to FIG. 12 of that patent it can be seen how the tubular rivet works as it is fastened in place. This device differs from the instant invention in that the materials are made from metal, albeit ductile metals, which means that the device is not reusable unless a new slotted sleeve is used each time. Furthermore, once the ductile material takes the configuration of the bottom surface of the work piece, there is no way that the device can be adjusted up or down and still give the maximum of security.
There are other significant features of the inventive device of the instant invention which makes it different from the patented device which differences will be set forth infra.
The fasteners of the instant invention are non-corroding. The fasteners of the instant invention protect the exposed metal surface of the metal deck to prevent corroding. The fasteners of the instant invention have backout and pullout resistance that are not found in the prior art devices. The fasteners of the instant invention can be easily adapted for a universal length through the thickness of the roof system. The fasteners of the instant invention provide an air seal to prevent air from entering the the hole in the deck, and finally, the fasteners of the instant invention provide a leak location mechanism utilizing the fasteners as the point of reference.
Thus, one object of the instant invention is to provide the simplest mechanism possible to provide the maximum holddown to maintain a deck system that is normally pierced by a fastener. A second object of the instant invention is to provide a non-corroadable fastener that can be used as a means of detecting leaks in a lamellar roof system, and a further object of this invention is to provide a detecting system for leaks that will allow for prohibition of air leakage from the interior of the building through the roof system to the outside because of the piercing of the laminates of the roof system. It should be noted that this device and method of securing roofs is especially useful for re-roofing over old lamellar roof systems because it allows one to re-insulate right over the old roof, apply an integral water impermeable membrane over the new insulation, and use the devices of the instant invention for fastening the whole into place over the old roof. This system allows one to reroof a building without tearing into the old roof.
These and other important objects will become evident to those skilled in the art by the reading and understanding of the instant specification and claims.